Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $58.63   6.314%   $62.3319   $62.33   $62.35   $62.30  
  Purchase #2 $66.80   10.233%   $73.6356   $73.64   $73.65   $73.60  
  Purchase #3 $57.66   5.319%   $60.7269   $60.73   $60.75   $60.70  
  Purchase #4 $173.66   6.795%   $185.4602   $185.46   $185.45   $185.50  
  Purchase #5 $149.94   8.397%   $162.5305   $162.53   $162.55   $162.50  
  Purchase #6 $214.94   8.366%   $232.9219   $232.92   $232.90   $232.90  
  Purchase #7 $209.73   5.364%   $220.9799   $220.98   $221.00   $221.00  
  7 purchase totals = $931.36       $998.5869   $998.59   $998.65   $998.50